At a termination end of a high power cable the high voltages will create electric fields and electrical stress, in particular at an outer shield of the cable. High voltage cables therefore need to have some type of stress relief device installed at the termination end thereof for handling these electrical stresses.
A stress cone is one type of such stress relief devices for controlling electric fields particularly at cable terminations, and is in many cases crucial for the functioning and robustness of cable terminations. The stress cones are typically made of two different rubber materials, e.g. semiconducting rubber and insulating rubber, where the shape and difference in material properties guide and distribute the electric field in order to minimize risks of insulation breakdown. A deflector, for instance made of semiconducting rubber, guides the electric field through insulating rubber with high breakdown strength.
In existing high power cable terminations, in particular in high voltage direct current (HVDC) terminations, the stress cone is installed over a field grading adapter in turn mounted over the cable end. A resistive field grading adapter comprising a field grading material redistributes the electric field through its field-dependent conductivity, wherein the electrical conductivity depends on the electric field. The stress cone also provides geometrical field grading in order to control the electric field during transients, such as impulses.